The present invention concerns a method for manufacturing watch dials obtained by processing "murrino" glass.
It is known that "murrino" glass or "murrina" is a glass product obtained by melting a plurality of small glass cylinders having a length of 5-6 mm and a diameter of 3-4 mm, placed next to each other, usually presenting different colour and arranged so as to form a pre-determined pattern. The small cylinders, arranged so as to form a pre-determined pattern are then melted in a glass-melting oven and the product resulting therefrom is called "murrina".
The "murrinas" as known at the present time are used essentially as pendants for necklaces or as medallions and they are usually round objects. The thickness which in the known technique measures 5-6 mm cannot be reduced because of the danger of breaking the murrina when further reducing its thickness with known techniques applied in the processing of artistic glass.
This limitation, i.e. the present impossibility of obtaining a thin thicknesses of "murrinas" has prevented the realization of a dial for watches obtained from a "murrina", since a dial with a thickness of 5-6 mm. could not be obtained, if one considers that this is the required thickness of a complete watch dial.
The present invention proposes a method for manufacturing watch dials using "murrino" glass, whereby the above mentioned inconveniences can be overcome.
More specifically, the purpose of the present invention is to provide a manufacturing method, whereby it is possible to produce watch dials of "murrino" glass having a thickness of about 1 mm or less, for example about 0.8 mm, without any danger of breaking the "murrino" glass, while obtaining smooth surfaces which are parallel to each other. The watch dials do not prevent the free rotation of the watch hands and do not impede the movement of the watch works on the underside of the dial. All of the above-mentioned purposes, which are better explained hereinafter, can be obtained by the method for manufacturing dials obtained by processing .-+.murrino" glass, said type of glass consisting of a disc having considerable thickness. The glass is obtained by melting a plurality of small glass cylinders arranged one next to the other so as to form a pattern, wherein said method is characterized in that is comprises:
a phase of axial drilling of the "murrina" disc in order to obtain a hole having such a diameter as to allow the passage of the hand-supporting shaft therethrough; PA0 one or more honing phases on the two surfaces of the "murrina" disc, to obtain a reduction in thickness in accordance with the intended use of the disc as a watch dial with two flat surfaces which are parallel to each other; PA0 a phase for trimming the outer edge of the "murrina", so as to obtain a desired outer perimeter and; PA0 a subsequent phase for polishing at least one of the two visible surfaces of the "murrina".
Advantageously according to the present invention, after the "murrina" disc has been axially drilled, the most delicate phase is undertaken where it consists of honing the surfaces of the "murrina", so as to obtain two flat and smooth surfaces which are parallel to each other and a thin thickness which is compatible with the use of the disc as a watch dial. The honing process is performed in at least two phases by means of a machine having a honing disc and a support for anchoring the "murrina". The support on which the "murrina" is anchored is brought close to the rotating honing disc and, by performing a tangential alternate motion between the "murrina" and the honing disc a first honing of one "murrina" surface and a first reduction of its thickness are obtained. When the thickness of the "murrina" is about twice the final desired thickness, the "murrina" is removed from the support which holds it on the machine head and it is turned downside up, so that it can be placed in the support with the already honed surface facing up and the surface to be honed turned face down toward the honing disc.
The fixed connection between the "murrina" and its support is obtained by means of a special bonding agent resisting to temperatures of up to 150.degree. to 250.degree. degrees C. When the "murrina" needs to be detached from its support, the bonding agent is heated and the "murrina" will come off the support.
Once the thickness has been thus reduced to a size which is compatible with the thickness of dials that can be used in normal wrist watches, the outer edge of the "murrina" disc will be trimmed and it can retain its round shape or acquire a square or rectangular or even any other shape.
Finally at least one of the two visible surfaces will be polished. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and the specific example, while indicating a preferred embodiment of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description, and from the drawings, wherein: